Nowadays, various electronic apparatuses incorporate communication devices that perform wireless transmission and reception of signals. Such communication devices include, for example, one that automatically adjusts and optimizes power of a transmission signal (hereinafter, transmission power).
A description will be given of a configuration of the above-mentioned conventional communication device with reference to FIG. 3. FIG. 3 is a block diagram showing the configuration of parts of the conventional communication device. As shown in FIG. 3, a communication device 100 includes: a modulator 101 for modulating transmission data; a transmission-side amplifier 102 for amplifying a signal modulated by the modulator 101; a transmission-side mixer 103 for mixing a signal of a predetermined frequency with a signal outputted from the transmission-side amplifier 102; a transmission-side oscillator 104 for inputting a signal of a predetermined frequency to the transmission-side mixer 103; a transmission-side band-pass filter (BPF) 105 for filtering out frequency components other than a predetermined frequency component from a signal outputted from the transmission-side mixer 103 to output the resultant signal; an automatic amplifier 106 for amplifying a signal outputted from the transmission-side BPF 105; an antenna BPF 107 for filtering out frequency components other than a predetermined frequency component from a signal inputted from the automatic amplifier 106 or a signal inputted from an antenna 108 (which will be described later) to output the resultant signal; an antenna 108 for wirelessly transmitting a signal (transmission signal) inputted via the antenna BPF 107 from the automatic amplifier 106 and for receiving a signal (reception signal) transmitted from a communication counterpart; a reception-side amplifier 109 for amplifying a signal inputted via the antenna BPF 107 from the antenna 108; a reception-side mixer 110 for mixing a signal of a predetermined frequency with a signal outputted from the reception-side amplifier 109; a reception-side oscillator 111 for inputting a signal of a predetermined frequency to the reception-side mixer 110; a reception-side BPF 112 for filtering out frequency components other than a predetermined frequency component from a signal outputted from the reception-side mixer 110 to output the resulting signal; and a demodulator 113 for demodulating the signal outputted from reception-side BPF 112 to acquire reception data.
The communication device 100 also includes an amplification degree setting portion 114 for setting the degree of amplification performed by the automatic amplifier 106 based on the power of the signal outputted from the reception-side BPF 112 (that is, the power from the reception signal; hereinafter, reception power). The amplification degree setting portion 114 sets the degree of amplification performed by the automatic amplifier 106 based on the reception power, and thereby achieves optimization of the transmission power. That is, the communication device 100, considering the reception signal and the transmission signal to be in the same condition, controls the transmission power based on the reception power.